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Transcript
12.3 Origin of Life
KEY CONCEPT
The origin of life on Earth remains a puzzle.
12.3 Origin of Life
Earth was very different billions of years ago.
• There have been many hypotheses of Earth’s origins.
• The most widely accepted hypothesis of Earth’s origins is
the nebula hypothesis.
12.3 Origin of Life
Several sets of hypotheses propose how life began on
Earth.
• There are two organic molecule hypotheses.
– Miller-Urey experiment
electrodes
“atmosphere”
water
“ocean”
heat source
– meteorite hypothesis
amino acids
12.3 Origin of Life
• There are different hypotheses of early cell structure.
– iron-sulfide bubbles hypothesis
12.3 Origin of Life
• There are different hypotheses of early cell structure.
– lipid membrane hypothesis
12.3 Origin of Life
• A hypothesis proposes that RNA was the first genetic
material.
– Ribozymes are RNA
molecules that catalyze
their own replication.
– DNA needs enzymes to
replicate itself.